Tagatose is an epimer of D-fructose, and has a natural sweet taste hardly distinguishable from sucrose and physical properties similar to sucrose. Tagatose is a natural sweetener, which is present in a small amount in food such as milk, cheese, cacao, and the like, and in sweet fruits such as apples and mandarin. Tagatose has a calorie value of 1.5 kcal/g which is one third that of sucrose, and a glycemic index (GI) of 3 which is 5% that of sucrose. Tagatose has a sweet taste similar to that of sucrose and various health benefits. In this regard, tagatose can be used as an alternative sweetener capable of satisfying both taste and health when applied to a wide variety of products.
It is known that tagatose can be produced from galactose by a chemical (catalytic reaction) method or a biological (isomerizing enzyme reaction) method (Korean Patent Laid-open Publication No. 2009-0082774, published on Jul. 31, 2009). In order to economically produce galactose as a raw material for the above reactions, studies have been made to develop various raw materials containing galactose, a method for attaining galactose and a method for producing tagatose using the raw materials. Lactose has been used as the most representative raw material for galactose. However, the price of lactose or lactose-containing products was unstable, depending on produced amounts, supply and demand of raw milk and lactose in global markets, and the like. Such price fluctuations disrupt stable supply of raw materials for producing tagatose.
Specifically, around 2012, sharp increase in global lactose price was mainly caused by rapid demand for skimmed milk powder and whole milk powder containing lactose due to rapid economic growth in China and decrease in annual milk production in dairy-producing countries due to global warming. Such price fluctuations in raw material price make stable production of tagatose difficult. Accordingly, there is a need for a new method for preparing tagatose using common saccharides (sucrose, glucose, fructose, and the like).